The present invention concerns novel lignosulfonic acid derivatives, their process of preparation and their use for the preparation of drilling and packer muds.
U.S. Pat. No. 3,087,923 describes a process for the transformation of lignosulfonate in such a way as to obtain products to be used as additives for drilling muds. It was mentioned therein that various oxidizing agents and wide operating conditions were able to be used although in practice the products always contained chromium or iron salts (or more generally multivalent metals) for which metallic derivatives play a determining role in the oxidizing process.
The present invention relates to the obtention of lignosulfonic acid derivatives which can be used as additives to fluids used for the drilling and completion of wells comprising the following steps:
heating at 115.degree. C. to 160.degree. C. in a closed container for a period of 1 to 30 minutes a mixture of a lignosulfonic acid aqueous solution having a pH lower than 3, containing 100 g to 600 g lignosulfonic acid per liter, and an oxidizing agent supplying 0.5 g to 2 g oxygen per 100 g lignosulfonic acid; PA1 neutralizing the product obtained by an alkaline solution having a pH at least equal to 3.5; PA1 possible drying of the product: PA1 reduction of the apparent and plastic viscosity of the slurries, PA1 reduction of thixotropy, PA1 increase of water retention capacity, the products according to the invention are at least as efficient as the known products while having an improved resistance to temperature.
The oxidizing agents are selected from among the multivalent metal free oxidizing agents group, such as hydrogen peroxide, ozonised oxygen, and alkaline chlorites and hypochlorites in such a way as to obtain lignosulfonic derivatives free of multivalent metal, such as chromium and iron.
The feed for the present invention is a lignosulfonic acid having a pH lower than 3. This acid is formed from a mixture of acids, product of the acidification of the lignosulfonates resulting from the black liquor of the paper-making process known as "the bisulphite process".
The acidification may be carried out by any known means such as the action of a strong acid generating an insoluble salt, for example, sulfuric acid in the case of calcium lignosulfonate, or as the passage of the product over an ion exchanger resin.
The lignosulfonic acid is used in the form of an aqueous solution containing 100 g to 600 g of acid per liter of solution; the pH value of such a solution is lower than 3 and often lower than 1.
The solution is mixed with a non-metallic oxidizing agent, supplying between 0.5 and 2 g oxygen per 100 g lignosulfonic acid. The mixture is brought to a temperature in the range of 115.degree. C. to 160.degree. C., in a pressure and corrosion resistant closed container.
The reaction is carried out continuously or discontinuously during 1 to 30 minutes according to the temperature, the concentration of the reactants and the properties sought from the reaction product. The reaction durations vary by inverse function to the temperature and/or concentration of the reactants--all other things being equal.
If the temperature is too high the product obtained, after cooling, is a rigid gel only slightly soluble in water. What is referred to above as the reaction duration, at a given temperature, is the period during which the mixture remains at the said temperature, taking into account the duration of heating, this heating preferably being carried out fairly quickly, and not taking into account duration of the cooling, which is carried out by circulation of a cooling fluid throughout the reactor.
At the end of the reaction and after cooling, the solution is at least partially neutralized; the purpose of this neutralization is to bring the pH from below 1 to a value at least equal to 3.5. This neutralization is carried out through use of a base, such as NaOH, KOH or, in certain specific cases, calcium or magnesium oxide.
The product may possibly be dried; the dried product has the appearance of a dark-coloured powder.
The products such as described herein-above may be used for example as additives for drilling and completion fluids, either in the form of the obtained aqueous solution, or in the form of a dry powder. They have the essential advantage, over currently known lignosulfonate-based products, of being free of heavy multivalent metals, and with respect to the other properties sought:
The following examples are given by way of illustration without in any way limiting the scope of the invention:
Examples 1 to 4 illustrate lignosulfonic acids modified by hydrogen peroxide.
Lignosulfonic acids is used in the form of an aqueous solution containing 100 g to 600 g acid per liter of solution; the pH of such a solution is about 1 or below.
The solution is mixed with the hydrogen peroxide used generally in the form of a 100 volumes solution (a solution such that, by decomposition are formed 110 normal liters of gaseous oxygen per liter of solution). 5 to 30 g of hydrogen peroxide at 110 volumes (or an equivalent quantity of oxygen at 110 volumes when the hydrogen peroxide occurs in another concentration) are used for 100 g lignosulfonic acid contained in the solution.